Miniature electronic ballast on the IR51HD420 chip. Scheme, description

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Electronic ballasts. Miniature electronic ballast on the IR51HD420 chip. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Ballasts for fluorescent lamps

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Another version of the miniature electronic ballast, made on the IR51HD420 hybrid chip, is shown in Fig. 3.24. The circuit is built on a half-bridge principle. The scheme has additional features:

setting the warm-up time for the incandescent electrodes of the lamp;
the presence of a protective mode of operation of the electronic ballast in case of burnout of incandescent electrodes and the absence of a lamp.

Scheme of two-stage heating of filament electrodes formed by elements R3-R5, C5, C7, VD2-VD4, VT1, VT2. The heating time of the filament electrodes is set by the elements R3, C5, VD2, VD3. The circuit works in the following way. At the initial moment, transistors VT1, VT2 are closed - the frequency of the driver and heating is determined by the elements R6, C6, C7, VD4. This frequency is higher than resonant, the voltage on the lamp is not enough to ignite it. As the capacitor C5 charges, the voltage across it increases. The first threshold element opens on the zener diode VD3, which in turn leads to the opening of the key element VT1.

After that, the driver frequency is determined by the elements R6, C6, C7. The process of heating the electrodes continues. Further, with an increase in voltage at C5, the second threshold element opens on the zener diode VD2, which, in turn, leads to the opening of the key element VT2. The driver frequency decreases (determined by the elements R6, C6) and becomes equal to the resonant frequency. The process of warming up the electrodes ends, the inductive resonant surge of voltage ignites the lamp.

Transistors VT1, VT2 are n-channel MOSFETs in SOT-23 package with parameters:

maximum drain current I_D -1,2 A;
impulse maximum drain current I_DM - 7,4 A;
maximum drain-source voltage V_DS - 20 V;
maximum power dissipation P_D - 540 mW;
resistance in the open state - 0,25 Ohm.

Protective mode of operation electronic ballast in case of burnout of incandescent electrodes and the absence of a lamp is implemented on a special way of powering IR51HD420. Elements SI, VD5, VD6 form a kind of feed circuit for the driver. Resistor R2 is selected in such a way that when the lamp is installed and working, together with the power supply circuit, sufficient current is generated for the driver to operate normally (the voltage at pin 1 is 13-15 V). But if the electrodes break or the lamp is absent, the feeding process is disrupted, the voltage at the supply pin 1 drops, the IR51HD420 microcircuit goes into a protective mode of operation, characterized by periodic blocking of the power switch control circuit.

The oscillogram of the protective mode of operation is shown in fig. 3.25 a. Voltages and currents on the electrodes of the lamp during warm-up, ignition and glow are shown in fig. 3.25 bd.

Rice. 3.24. Scheme of a miniature electronic ballast on the IR51HD420 chip (click to enlarge)

Miniature electronic ballast on the IR51HD420 chip
Rice. 3.25. Oscillograms explaining the operation of the electronic ballast: a - voltage at the output of the half-bridge switch with the lamp turned off (faulty); b - voltage at the cathode of a fluorescent lamp; c - current through the cathode of the lamp; g - voltage on the lamp; d - lamp current

The inductor of the electronic ballast L2 is made on a W-shaped magnetic core made of M2000NM ferrite. Core size Sh5x5 with a gap δ = 0,4 mm. Winding L2 - 205 turns of PEV-2 wire with a diameter of 0,2-0,25 mm. Interlayer insulation - varnished cloth. Winding - turn to turn.

This electronic ballast is designed to work with a compact fluorescent lamp with a power of 13 W, a current of 0,165 A and a resistance of 4 ohm filament electrodes in a cold state.

Author: Koryakin-Chernyak S.L.

See other articles Section Ballasts for fluorescent lamps.

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